Polymerization solvent effects

Zentner, G. M., Cardinal, J. R., and Gregonis, D. E., 1979, Progestin permeation throirgh polymer membranes III Polymerization solvent effect on progesterone permeation through hydrogel membranes, J. Pharm. Sci 68(6) 794-797. 

Table 2. Effect of Polymerization Solvent on Polyisoprene Microstmcture...

Collins and coworkers applied the bis(tetrahydroindenyl)zirconium triflate 32, which is used as a polymerization catalyst, to the asymmetric Diels-Alder reaction [50] (Scheme 1.61). A remarkable solvent effect was observed - although only a low optical yield was obtained in CH2CI2, high optical purity (91% ee) was realized in 2-nitropropane by use of only 1 mol% of the catalyst. The catalyst is also effective for crotonoyloxazolidinone, giving the cycloadduct in 90% ee. 

Photoinitiation of polymerization of MMA and styrene by Mn(facac)3 was also investigated, and it was shown that the mechanism of photoinitiation is different [33] from that of Mn(acac)3 and is subject to the marked solvent effect, being less efficient in benzene than in ethyl acetate solutions. The mechanism shown in Schemes (15) and (16) illustrate the photodecomposition scheme of Mn(facac)3 in monomer-ethyl acetate and monomer-benzene solutions, respectively. (C = manganese chelate complex.)... 

The reactivity of macromonomers in copolymerizalion is strongly dependent on the particular comonomer-macromonomer pair. Solvent effects and the viscosity of the polymerization medium can also be important. Propagation may become diffusion controlled such that the propagation rate constant and reactivity ratios depend on the molecular weight of the macromonomer and the viscosity or, more accurately, the free volume of the medium. 

Solvent effects on radical polymerization have been reviewed by Coote and Davis,59 Coote et. Barton and Borsig,71 Gromov,72 and Kamachi" 1 A summary of kinetic data is also included in Beuennann and Buback s review.74 Most literature on solvent effects on the propagation step of radical polymerization deals with influences of the medium on rate of polymerization. 

One of the most dramatic examples of a solvent effect on propagation taken from the early literature is for vinyl acetate polymerization.78,79 Kamachi el al.n reported a ca. 80-fold reduction in kp (30aC) on shifting from ethyl acetate to benzonilrile solvent (Table 8.1). Effects on polymer structure were also reported. Hatada ef a m conducted a H NMR study on the structure of the PVAc formed in various solvents. They found that PVAc (M n 20000) produced in ethyl acetate solvent has 0.7 branches/chain while that formed in aromatic solvents is essentially unbranched. 

The solvent in a bulk copolymerization comprises the monomers. The nature of the solvent will necessarily change with conversion from monomers to a mixture of monomers and polymers, and, in most cases, the ratio of monomers in the feed will also vary with conversion. For S-AN copolymerization, since the reactivity ratios are different in toluene and in acetonitrile, we should anticipate that the reactivity ratios are different in bulk copolymerizations when the monomer mix is either mostly AN or mostly S. This calls into question the usual method of measuring reactivity ratios by examining the copolymer composition for various monomer feed compositions at very low monomer conversion. We can note that reactivity ratios can be estimated for a single monomer feed composition by analyzing the monomer sequence distribution. Analysis of the dependence of reactivity ratios determined in this manner of monomer feed ratio should therefore provide evidence for solvent effects. These considerations should not be ignored in solution polymerization either. 

ESI mass spectrometry ive mass spectrometry ESR spectroscopy set EPR spectroscopy ethyl acetate, chain transfer to 295 ethyl acrylate (EA) polymerizalion, transfer constants, to macromonomers 307 ethyl methacrylate (EMA) polymerization combination v.v disproportionation 255, 262 kinetic parameters 219 tacticity, solvent effects 428 thermodynamics 215 ethyl radicals... 

Lipase-catalyzed polymerizahon of oxyacid esters was reported. PPL catalyzed the polymerizahon of methyl 6-hydroxyhexanoate. ° The polymer with DP up to 100 was synthesized by polymerization in hexane at 69°C for more than 50 days. The PPL-catalyzed polymerization of methyl 5-hydroxypentanoate for 60 days produced the polymer with DP of 29. Solvent effects were... 

Table II. Solvent Effects on the Polymerization of Dichloro-di-n-Hexylsilane...

---